Cannabis use is associated with other substance use and misuse, mental illness, cognitive impairment, lower educational attainment, and higher unemployment. Additionally, cognitive and psychosocial impairments are more pronounced among early-onset cannabis users compared to late-onset users and among female users compared to male users. But it is unclear if these associations reflect a causal influence of cannabis, given that most studies are cross-sectional, and almost all are correlational. Thus, rather than cannabis causing functional impairments, it is possible that cannabis' users functional deficits predate their drug use and that unmeasured factors are responsible for both individuals' cannabis use and their impaired functioning. The proposed study seeks to strengthen the basis for causal inference through the use of a longitudinal and genetically informative sample and a combination of powerful and innovative methods designed to elucidate causal claims. The specific aims of the proposed project are threefold: (1) to examine the adult (ages 20-29) cognitive, psychiatric, and educational/occupational outcomes associated with youth cannabis use, while testing if gender moderates the strength of observed associations; (2) to use a potent co-twin control design in combination with propensity scores to remove the effects of genetic and environmental factors that confound the relation between youth cannabis use and adult outcomes; and (3) to examine if youth cannabis use modifies risk for adult psychiatric and cognitive outcomes by moderating the magnitude of genetic and environmental effects on these outcomes. The applicant and her sponsor have carefully devised a training plan that will equip the applicant with the skills necessary to complete the proposed study and to develop into an independent research scientist. In completing the proposed research, the applicant will benefit from the significant mentorship experience and research expertise of her sponsor as well as the many, outstanding resources available at the Minnesota Center for Twin and Family Research. The proposed project represents the first comprehensive and systematic investigation into the causal basis of associations between youth cannabis use and adult outcomes across multiple domains of functioning, and it arrives at a time of important decision-making about cannabis decriminalization and legalization in several U.S. states.